A widget which displays items in a one- or two-dimensional arrangement.
Items have a parent-child relationship with other items. Items have a
set of states, which are boolean properties. Items may be spread about
one or more columns. For each column of an item there is a style
associated, which determines how to display the item's column taking
into account the item's current state set. One column can be defined to
display the data in a hierarchical structure.

Additional documentation, with examples and pictures:
http://tktreectrl.sourceforge.net/Understanding%20TkTreeCtrl.html
